Recent studies have emphasized the limitations of conventional coronary angiography. These limitations include the large intraobserver and interobserver variability that result from subjective visual grading of coronary stenotic lesions. Furthermore, pathologic findings have shown a lack of correlation between the severity of coronary stenosis as estimated from coronary angiograms and the actual severity of stenotic lesions measured in postmortem hearts. As a result, attempts have been made to quantitate luminal dimension more precisely. The application of quantitative digital subtraction angiography (DSA) in the assessment of coronary artery lesion dimension has been limited by cardiac and respiratory motion. The purpose of this research plan is to develop and apply in patients a motion immune dual-energy digital subtraction technique which will provide a videodensitometric technique for the assessment of absolute coronary arterial cross-sectional area. More specifically, the aims are: First, to design and implement a motion immune dual- energy mode for human cardiac imaging. This dual-energy coronary angiography mode will produce contrast enhanced digital subtraction images without producing motion misregistration or background tissue artifacts. Secondly, the physical degradation factors limiting the application of digital subtraction images for assessment of various physiological parameters will be investigated. The physical degradation factors that will be investigated are scatter and veiling glare, spectral beam hardening, image distortion, detector non-uniformity and heel effect. Thirdly, a videodensitometric analysis of dual-energy subtraction images will be investigated to test the hypothesis that absolute coronary arterial cress-sectional area can be measured independent of geometric assumptions. The videodensitometric analysis will be performed on dual-energy (as opposed to temporal) subtraction images and will produce absolute (as opposed to relative) cross-sectional area of coronary arteries. Finally, the developed algorithms will be automated so the quantitative measurements can be performed in a short time period with minimal operator intervention. The results of this research will provide improved methods of quantitating coronary artery lesion dimension in patients, using dual-energy digital subtraction angiography. Furthermore, the basic data set from these quantitative techniques can potentially be utilized to derive more physiologically significant parameters such as absolute blood flow or coronary blood flow reserve.